Telescope Reviews: Why no commercial source for "Duncan" Mask?

· Get a Cloudy Nights T-Shirt

· Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

You are not logged in. [Login]

Entrance · Main Index · Search · New user · Who's Online
FAQ · Calendar

Equipment Discussions >> Cats & Casses

Pages: 1 | 2 | 3 | 4 | (show all)

jrbarnett
Eyepiece Hooligan

Reged: 02/28/06

Loc: Petaluma, CA

Why no commercial source for "Duncan" Mask?
#5346779 - 08/01/12 11:08 AM

Most of you probably know what a Duncan Mask is. For those that don't, it's a collimation tool for catadioptrics conceived of by UK amateur Duncan Evenden. It consists of an aperture mask with cut-outs opposite of the collimation screws. Here's an example together with basic instructions on its use:

http://stargazerslounge.com/index.php?app=core&module=attach&section=attach&attach_id=65090

My question is this. Given the exorbitant prices fetched for SCT collimation tools like the Hotech unit, why hasn't any commercial producer bothered to manufacture Duncan Masks for commercial SCTs? Heck, Celestron and Meade could *include* them with their scopes. Producing a solidly mounted, precision mask would literally cost pennies.

Orion? Astrozap? Scopestuff? Are you listening?

- Jim

Post Extras:

brianb11213
Postmaster

Reged: 02/25/09

Loc: 55.215N 6.554W

Re: Why no commercial source for "Duncan" Mask? new

[Re: jrbarnett]
#5346851 - 08/01/12 11:40 AM

Quote:

Heck, Celestron and Meade could *include* them with their scopes. Producing a solidly mounted, precision mask would literally cost pennies.

For a few pennies they could upgrade the power cord connector to a reliable type.

For a few dollars they could stick a dew shield in the retail box (SCTs and Maks are essentially useless without a dewshield) and add forced ventilation fans.

These companies are more interested in what they can pay their shareholders now than in whether or not they have a repeat customer in five years.

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: brianb11213]
#5346934 - 08/01/12 12:36 PM

I was thinking of making one of those masks, do they work and if they do does it get collimation spot on ?

Post Extras:

bilgebay
Post Laureate

Reged: 11/06/08

Loc: Türkiye - Istanbul and Marmari...

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5347114 - 08/01/12 02:36 PM Attachment (57 downloads)

I built one for my C11 but didn't like it as the pattern it produced was too dim. Maybe I didn't understood the formula and made a mistake during the design phase. I will produce another one asap.

Post Extras:

gnowellsct
Postmaster

Reged: 06/24/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: jrbarnett]
#5347290 - 08/01/12 04:44 PM

Quote:

My question is this. Given the exorbitant prices fetched for SCT collimation tools like the Hotech unit, why hasn't any commercial producer bothered to manufacture Duncan Masks for commercial SCTs? Heck, Celestron and Meade could *include* them with their scopes. Producing a solidly mounted, precision mask would literally cost pennies.

Orion? Astrozap? Scopestuff? Are you listening?

- Jim

Jim, they don't bring out product because they know they can't beat the Sheer Genius Collimation Device.

It's priceless.

http://www.astromart.com/articles/article.asp?article_id=718

Greg N

Post Extras:

gnowellsct
Postmaster

Reged: 06/24/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: gnowellsct]
#5347328 - 08/01/12 05:04 PM

There's a close up in this thread.

sheer genius collimation device

Post Extras:

bluedandelion
Carpal Tunnel

Reged: 08/17/07

Loc: Hazy Hollow, Western WA

Re: Why no commercial source for "Duncan" Mask? new

[Re: gnowellsct]
#5348049 - 08/02/12 01:13 AM

You should have said, "The SGCD is so simple, it cannot be invented. I am not the inventor."

The uses of a stick are many, but how does one invent one? You found a new use for an old device.

Ajay

Edited by bluedandelion (08/02/12 01:15 AM)

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: bilgebay]
#5348290 - 08/02/12 08:02 AM

Quote:

I built one for my C11 but didn't like it as the pattern it produced was too dim. Maybe I didn't understood the formula and made a mistake during the design phase. I will produce another one asap.

I think it should be a round disc with 3 cutouts In the shape of the grey area, it should look like a 11" cats eye hotspot
http://i1172.photobucket.com/albums/r563/nev19/ccd762f7.jpg

Edited by BRisley (08/02/12 10:26 AM)

Post Extras:

jmiele
Patron Saint?

Reged: 12/04/10

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5348332 - 08/02/12 08:39 AM

Exactly. The grey is what should make up the mask. Light grey that is.

Also the edge should account for the retaining ring so as not to make the 3 arc's become to slender.

Joe

Post Extras:

Mary B
Vendor - Echo Astronomy and Electronics

Reged: 05/21/10

Loc: Minnesota

Re: Why no commercial source for "Duncan" Mask? new

[Re: jmiele]
#5348994 - 08/02/12 04:27 PM

Be easy to laser cut, what is the math behind it?

Post Extras:

gnowellsct
Postmaster

Reged: 06/24/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: bluedandelion]
#5349074 - 08/02/12 05:11 PM

Quote:

You should have said, "The SGCD is so simple, it cannot be invented. I am not the inventor."

The uses of a stick are many, but how does one invent one? You found a new use for an old device.

Ajay

No no Ajay, I didn't invent "the stick." I invented *the properly placed notch*! (TM)

Greg N

Post Extras:

shiner
super member

Reged: 11/04/11

Loc: England

Re: Why no commercial source for "Duncan" Mask? new

[Re: gnowellsct]
#5368338 - 08/14/12 01:10 PM

I'm going to look into making one of these. The lid of a five gallon plastic paint tub should do the trick....

Post Extras:

Starhawk
Post Laureate

Reged: 09/16/08

Loc: Tucson, Arizona

Re: Why no commercial source for "Duncan" Mask? new

[Re: shiner]
#5369406 - 08/15/12 01:30 AM

I've used the shadow of my arm in place of the stick.

It works. I think the reason no one makes one is it's like trivial. Print out a radiation warming symbol and get some scissors.

-Rich

Post Extras:

jrbarnett
Eyepiece Hooligan

Reged: 02/28/06

Loc: Petaluma, CA

Re: Why no commercial source for "Duncan" Mask? new

[Re: Starhawk]
#5370133 - 08/15/12 01:21 PM

You mean "trivial" like commercially available flexible dew shades, Bob's Knobs, magnetic "speaker magnet" counterweights, Baader solar film ring filters, "shower cap" style solid tube Dob end caps, collimation caps, etc.?

There are loads of things that are utterly trivial to make yourself, yet they sell well when made available commercially. I would also like to see "stop down" dust caps for refractors with threaded concentric rings allowing reduction in aperture in 5mm increments (and corresponding extension of focal ratio).

Regards,

Jim

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5371142 - 08/16/12 06:52 AM

I made one yesterday (20 minutes with an X-acto knife and a piece of photo matte board), and got to try it last night. I am very excited by how well it worked! I did have decent seeing, and my scope was within 2°F of ambient temp when I pulled it out of the shed. I used a 5mm EP on my C11 for 560x, and even then the pattern of three lines was pretty small. I could easily see the effect on the pattern of tiny movements of the collimation screws. I think I achieved the best collimation I've ever had for my C11. I don't think I'd be overreaching to say that the Duncan mask is to collimating an SCT what a Bahtinov mask is to focusing my camera, at least for me. It gives the same kind of feedback anyway. I'm sure that the purists out there that are blessed with consistently good seeing can get perfect collimation without a mask, but the feedback it gives is a huge help to me. I leaves me wondering...why did I just now find out about this? And what other wonderful tricks are hidden out there?

Steve

Post Extras:

Pinbout
Post Laureate

Reged: 02/22/10

Loc: Montclair

Re: Why no commercial source for "Duncan" Mask? new

[Re: Mary B]
#5371948 - 08/16/12 05:46 PM Attachment (25 downloads)

Quote:

Be easy to laser cut, what is the math behind it?

if you send me one for 8in I'll tell you the math...

Post Extras:

elwaine
Pooh-Bah

Reged: 06/18/06

Loc: S.W. Florida

Re: Why no commercial source for "Duncan" Mask? new

[Re: Pinbout]
#5372092 - 08/16/12 07:41 PM

Good point Jim. A mask like that will certainly sell.

So which one of you guys are going to commercialize this?

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: elwaine]
#5372122 - 08/16/12 08:21 PM

I'd buy one for a C11, hint, hint, hint.....

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5372129 - 08/16/12 08:32 PM

http://stargazerslounge.com/index.php?app=core&module=attach&section=attach&attach_id=65090

With the above link you come across this sentence: "When they all meet collimation is achieved, when they cross evenly you are in perfect focus." I'm confused by it's meaning and hoping someone can clarify.

Would the sentence above be more accurate if it was written this way? "When the lines start to meet, collimation is almost achieved. When they all cross evenly, like the last picture, that is when you have achieved perfect collimation."

Thanks
Bart

Post Extras:

barasits
sage

Reged: 06/12/11

Loc: Chicago

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5372430 - 08/17/12 12:37 AM

Thanks for the report, Steve. You've convinced me to put this at the top of my project list.

Geoff

Post Extras:

OzAndrewJ
professor emeritus

Reged: 11/30/10

Re: Why no commercial source for "Duncan" Mask? new

[Re: gnowellsct]
#5372467 - 08/17/12 01:19 AM Attachment (36 downloads)

Gday Greg

Quote:

Jim, they don't bring out product because they know they can't beat the Sheer Genius Collimation Device.

It's priceless.

Unless you have bicycle spokes

About 5c each.
This allows you to adjust the collimation easily whilst looking through the EP and no risk of hitting the corrector with your fingers or allen keys etc.

Andrew

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5372731 - 08/17/12 08:37 AM

Bart asks "Would the sentence above be more accurate if it was written this way? "When the lines start to meet, collimation is almost achieved. When they all cross evenly, like the last picture, that is when you have achieved perfect collimation."

No. As you approach focus, whether collimated or not, the three little spikes (produced by diffraction through the three open arcs) converge. If you have ever used a Hartmann mask it behaves the same way. If you are collimated, the three little spikes all arrive at the center at the same time. Conveniently, there is a tiny dot at the point where they converge, presumably the Airy disk of the star. If you are not quite collimated the spikes do not arrive at the same time. In my case, two of the three spikes touched the dot together while the third spike hadn't quite made it. Luckily it was the spike at the 12:00 (or 6:00) position so I knew which knob (Bob's) to turn. I gave the "top" knob maybe 1/8th of a turn. Checking the spikes again the errant spike now reached the dot before the other two, so I knew I had gone too far. I moved the top knob back a little at a time, checking the spikes' behavior, until they appeared to arrive at the dot in unison. By "checking the spikes' behavior" I mean making small movements of the focus knob and watching the spikes move radially towards or away from the little central dot.

Edited by Steve OK (08/17/12 08:39 AM)

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5372769 - 08/17/12 09:06 AM

I guess I'm getting confused with the idea of collimation and focusing being the same thing.

So as represented with the third picture, second from right, when all the lines converge at the beginning of the lines, collimation has been achieved. Then when you focus, the lines move on top of each other as suggested in pic number four, first from right. Is that correct?

Thanks
Bart

Post Extras:

HeyJP
sage

Reged: 12/11/10

Loc: Boulder, CO

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5372812 - 08/17/12 09:42 AM

Now you have it, Bart. When you collimate,, you intentionally de-focus your scope, then adjust the collimation screws until an endpoint of the three lines just touch in the center. You can then re-focus your scope which causes the three lines to overlap and cross their centers.

Jim

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: HeyJP]
#5372861 - 08/17/12 10:14 AM

Thanks.

Post Extras:

elwaine
Pooh-Bah

Reged: 06/18/06

Loc: S.W. Florida

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5373590 - 08/17/12 05:41 PM

Does anyone know if a cheapo video eyepiece (made by Orion) is good enough to use with a Duncan mask?

Post Extras:

jrbarnett
Eyepiece Hooligan

Reged: 02/28/06

Loc: Petaluma, CA

Re: Why no commercial source for "Duncan" Mask? new

[Re: OzAndrewJ]
#5376553 - 08/19/12 08:29 PM

Now *that* truly is sheer genius. Makes the stick look, well, unimaginative and rather antiquated.

- Jim

Edited by jrbarnett (08/19/12 08:30 PM)

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: jrbarnett]
#5379453 - 08/21/12 01:53 PM

I made one today for a C11 out of cardboard , I wasn't to sure of measurements so I guesstimated and this is what I came up with
[image]http://

[/image]
If it works , I'll make one from 1/4" plywood.

Edited by nevy (08/21/12 01:55 PM)

Post Extras:

end
super member

Reged: 08/31/11

Loc: Houston, Texas

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5379474 - 08/21/12 02:03 PM

Looks great! I will be very interested to hear how well this works. In particular I'm interested to know how fine of collimation can be achieved. In my opinion there are many ways to get rough or good collimation, but the final adjustment to very good or great collimation is much more difficult and usually involves analysis of a sharply focused star and its airy disk.

Post Extras:

gnowellsct
Postmaster

Reged: 06/24/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: OzAndrewJ]
#5379554 - 08/21/12 03:14 PM

Quote:

Gday Greg

Quote:

Jim, they don't bring out product because they know they can't beat the Sheer Genius Collimation Device.

It's priceless.

Unless you have bicycle spokes
About 5c each.
This allows you to adjust the collimation easily whilst looking through the EP and no risk of hitting the corrector with your fingers or allen keys etc.

Andrew

Those are very clever, though from the point of view of indicating which screw needs adjustment you need one shadow. Three would be confusing.

Greg N

Post Extras:

OzAndrewJ
professor emeritus

Reged: 11/30/10

Re: Why no commercial source for "Duncan" Mask? new

[Re: gnowellsct]
#5379656 - 08/21/12 04:11 PM

Gday Greg

Quote:

Those are very clever, though from the point of view of indicating which screw needs adjustment you need one shadow. Three would be confusing.

I dont use a finger/arm shadow.
Once you understand which way the star needs to be moved in the FOV when collimating, you just try each spoke to find the one that best fits the direction required.

Andrew

Post Extras:

Pinbout
Post Laureate

Reged: 02/22/10

Loc: Montclair

Re: Why no commercial source for "Duncan" Mask? new

[Re: OzAndrewJ]
#5379690 - 08/21/12 04:39 PM

Can you put little rubber angry birds on the ends of the spokes to make them look more imaginative?

Post Extras:

barasits
sage

Reged: 06/12/11

Loc: Chicago

Re: Why no commercial source for "Duncan" Mask? new

[Re: elwaine]
#5379866 - 08/21/12 06:43 PM

Larry, I hope you'll post a report on the Duncan mask and Orion eyepiece video cam combination. I think you're on the right track.

Geoff

Post Extras:

Gavin Bray
sage

Reged: 12/31/06

Loc: Australia

Re: Why no commercial source for "Duncan" Mask? new

[Re: barasits]
#5381624 - 08/22/12 07:25 PM

I made a Duncan mask and tested it last night. A little while ago I'd collimated using CCD Inspector and I believe my collimation is reasonably good. The Duncan mask worked as described. I tried an eyepiece at 355x but found the image to be fairly small and a little hard to discern the relative positions of the three bars. I then barlowed this up to 711x but of course things were bouncing around a bit. However, as far as I could tell, my collimation was fine. I also tried with a Lodestar guide camera and feel it or something similar could be used to make adjusting and checking collimation a lot easier.

Regards
Gavin

Post Extras:

elwaine
Pooh-Bah

Reged: 06/18/06

Loc: S.W. Florida

Re: Why no commercial source for "Duncan" Mask? new

[Re: Gavin Bray]
#5381730 - 08/22/12 08:39 PM

Hi Gavin,

Thank you for that report.

Quote:

The Duncan mask worked as described.

Was the collimation equal to, or better than the collimation you achieved with CCD Inspector?

Regards,

Post Extras:

Gavin Bray
sage

Reged: 12/31/06

Loc: Australia

Re: Why no commercial source for "Duncan" Mask? new

[Re: elwaine]
#5381791 - 08/22/12 09:13 PM

Hi Larry

The collimation looked good to me so I didn't make any adjustments.

It was relatively easy to make the mask though I'm not sure if it's quicker or more accurate than CCDI.

I'd certainly recommend making one and trying for yourself.

Regards
Gavin

Post Extras:

Adam E
Pooh-Bah

Reged: 06/29/09

Loc: Orlando, FL

Re: Why no commercial source for "Duncan" Mask? new

[Re: Gavin Bray]
#5382214 - 08/23/12 06:36 AM

Apologies if everyone already knows about this collimation / focusing aid, but anyone have any personal experience with one of these (GoldFocus)?

Post Extras:

elwaine
Pooh-Bah

Reged: 06/18/06

Loc: S.W. Florida

Re: Why no commercial source for "Duncan" Mask? new

[Re: Adam E]
#5382282 - 08/23/12 08:25 AM

Quote:

Apologies if everyone already knows about this collimation / focusing aid, but anyone have any personal experience with one of these (GoldFocus)?

No experience with that mask, but in reading about it on their website I note that it has to be used with a CCD camera... which in turn requires a computer, etc.. The Duncan Mask is simpler to use, requiring only a high power eyepiece.

I've made a Duncan Mask for my C9.25. It is very easy to make. I used black foam board that I bought at Office Depot. The foam board is flat black, fairly ridged, and very easy to cut with an Exacto knife. However, the night time clouds may not clear SW Florida skies for another month. (Hurricane Isaac will definitely ruin the next week or two.) So I hope others continue to report on their experiences with the Duncan Mask.

Post Extras:

BlueGrass
Carpal Tunnel

Reged: 07/25/09

Loc: Wasatch Front, UT

Re: Why no commercial source for "Duncan" Mask? new

[Re: Adam E]
#5384079 - 08/24/12 08:01 AM

Adam,
Thanks for the post and link. This looks very interesting. I've often found the accuracy of my various Bahtinov masks can depend on a number of things... most notably my eye's own ability to focus depending on how tired I am ...

If I read the web site correctly, the mask can be used without the analysis software...?

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: BlueGrass]
#5384224 - 08/24/12 10:06 AM

I've noticed a few people saying the image is a little dim with the Duncan mask, so I was thinking would the image be brighter if the depth of the 3 slits was a little deeper to allow more light of the star in ?

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5384264 - 08/24/12 10:24 AM

The image might be dim on smaller scopes. With my C11, it was plenty bright...using Vega as the star. I'm thinking that making the openings wider might make the pattern less distinct. As easy as the mask is to make, it might be worth an experiment!

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5384356 - 08/24/12 11:12 AM

Quote:

The image might be dim on smaller scopes. With my C11, it was plenty bright...using Vega as the star. I'm thinking that making the openings wider might make the pattern less distinct. As easy as the mask is to make, it might be worth an experiment!

Hello Steve , I havnt had a chance to try mine yet , I just guessed the measurements for mine , I also have a C11 , would you be so kind as to tell me what the measurements are for the slits ( ie the depth of the slits between the edge of the plastic ring on the corrector to the edge of the slit on the mask also the length of the slits ) Thanks.

Edited by nevy (08/24/12 11:23 AM)

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5384537 - 08/24/12 12:47 PM Attachment (75 downloads)

Here is what mine looks like. The measurements shown are the radii from the center to each relevant point. I divided the circle into 60° segments, then used a drawing compass to make the circles all from the same center. There is really no reason to leave the 10mm "ring" all the way around, but I think it is a good idea to cut the overall diameter to fit just inside the front ring. That way the mask rests on the corrector retaining ring, rather than the corrector itself. Hope this helps...let me know!

Steve

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5384580 - 08/24/12 01:15 PM

That's perfect , thankyou very much Steve

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5385238 - 08/24/12 08:48 PM

Steve,

Thanks for the instructions. I assume that's for the C11?

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5385876 - 08/25/12 06:46 AM

Hey, Bart...yes it is for the C11. It could be scaled proportionately for any size. I don't think these dimensions are all that critical, really. The diameter of the inner circle should allow an easy fit over the secondary housing with little slop, and the outer diameter should fit inside the front ring of the scope without binding.

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5385963 - 08/25/12 09:18 AM

Thanks, I'm going to make one.

Post Extras:

RodShea
member

Reged: 11/01/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5390366 - 08/27/12 08:17 PM

Not to hijack the thread, but this would work on other cassegrains as well?

Thanks,

Rod

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: RodShea]
#5390924 - 08/28/12 06:37 AM

I made one for my little C130 Mak-Cass. It seemed to work just as well as with my C11.

Post Extras:

RodShea
member

Reged: 11/01/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5392629 - 08/29/12 03:46 AM

Thanks,

Rod

Post Extras:

stuart keenor
member

Reged: 02/20/11

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5393702 - 08/29/12 05:33 PM

Quote:

I made one for my little C130 Mak-Cass. It seemed to work just as well as with my C11.

sound intresting may do the 10" mak cass!!what do you guys think? stuy

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5394466 - 08/30/12 08:24 AM

Since it only takes 20 minutes and costs little or nothing to make, why not?

Post Extras:

stuart keenor
member

Reged: 02/20/11

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5394887 - 08/30/12 12:52 PM

Quote:

Since it only takes 20 minutes and costs little or nothing to make, why not?

going to have a shot will let you know thanks stuy

Post Extras:

frolinmod
Pooh-Bah

Reged: 08/06/10

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5402540 - 09/04/12 09:10 AM

Steve, I made one just like yours, but the three arcs did not become lines as focus was moved in. They stayed arcs all the way to focus and I did not get crossed lines at focus. With that in mind, doing it with the mask did not make collimation any easier than doing it without the mask. I'll have to try one more time before making a new mask in the shape as shown by pinbout and nevy.

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: frolinmod]
#5402806 - 09/04/12 11:35 AM

I made a new one using Steves diamentions
[image]http://

[/image]
[image]http://

[/image]
The silver lines are so I can line them up with the collimation screws,
It did work as its suppose to , I thought my collimation was spot on using a star test ( concentric rings) , with the mask on , the lines crossed in the centre but one was slightly back a little bit so I adjusted it so they were all the same , I then took the mask off and looked at the defocused star , it showed not concentric rings (off to one side slightly ) so I collimated it back to perfect again without the mask , but then the clouds rolled in and had to cover the scope. I don't know why the two methods didn't agree , I'll have a go with it another time and try again . I found the lines to be bright enough but a bit awkward to see as they were very small ( I was using a 7.4 & 6.4mm eyepieces , 378x & 437x mag ) should I be using more power to make the image bigger?

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: frolinmod]
#5402953 - 09/04/12 01:01 PM

Well, Frolinmod, I don't know what to tell you. How was the seeing when you tried this? My first try with the mask happened to coincide with some (rare) good seeing. In subsequent trials with more average seeing, the pattern has been less distinct. But in all the trials, the arcs do in fact become tiny radial lines just before focus is reached. High power is required to see them. I was using 560x on my C11 the first time.

And to Nevy, I got a little taste of that myself, trying to collimate using my webcam. The two patterns with and without the mask did not agree. I started wondering if having a not-perfectly-centered secondary could cause such a discrepancy. I can't quite get my mind around it. I'll keep messing with the mask, no doubt, but perhaps the tried and true "center the airy disk in the diffraction rings" will win out after all.

Thanks for the feedback, guys!

Steve

Post Extras:

stuart keenor
member

Reged: 02/20/11

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5403387 - 09/04/12 04:28 PM

Quote:

Quote:

Since it only takes 20 minutes and costs little or nothing to make, why not?

going to have a shot will let you know thanks stuy

made one out of cardboard worked very well on the intes micro mak cass ingenious

stuy

Post Extras:

Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5403416 - 09/04/12 04:43 PM

Good news! Thanks for the report, Stuy.

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5403486 - 09/04/12 05:29 PM

I was wundering about the secondary not being centred , sometimes when I've did star tests before , I have noticed that although I get nice concentric rings , now & again I think I'm noticing the tiny dot right in the centre might not quite be in the dead centre. But sometimes it looks like it is , I'm not sure if I'm convincing myself it is centred becaus I bellieve it should be.

Post Extras:

Mary B
Vendor - Echo Astronomy and Electronics

Reged: 05/21/10

Loc: Minnesota

Re: Why no commercial source for "Duncan" Mask? new

[Re: barasits]
#5556391 - 12/05/12 08:41 PM

Added them to my product line!

Post Extras:

barasits
sage

Reged: 06/12/11

Loc: Chicago

Re: Why no commercial source for "Duncan" Mask? new

[Re: Mary B]
#5556490 - 12/05/12 09:47 PM

Quote:

Added them to my product line!

Great! I haven't had the time to make my own Duncan mask, so would you please provide a link to your web site.

Geoff

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: barasits]
#5558487 - 12/06/12 11:30 PM

Ditto! I'd love to pick one up for a C11.

Post Extras:

Mary B
Vendor - Echo Astronomy and Electronics

Reged: 05/21/10

Loc: Minnesota

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5558648 - 12/07/12 03:03 AM

No web site, send me a PM here. I found a web site was costing me more than I was making, this is a very small part time business. I will need dimensions of your scope in order to cut one. Scopes over 10 inches I have to farm out the cutting to someone with a larger laser and it isn't cheap.

Post Extras:

A. Viegas
sage

Reged: 03/05/12

Loc: New York City/ CT

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5561154 - 12/08/12 04:27 PM

I have a friend who has a new 3D printer. I will see if we can figure out how to print one of these Duncan masks for my C8 and C11... already printed out Bahtinov masks, so should not be that difficult.

Ideally, if anyone has a .svg file with exact dimensions for the Duncan mask, that would make it easier, otherwise I will use the drawings from a few of the posts on this thread. ( I assume there is no "Duncan Mask" generator on the web? http://astrojargon.net/MaskGenerator.aspx)

Al

Post Extras:

jbalsam
member

Reged: 07/06/12

Re: Why no commercial source for "Duncan" Mask? new

[Re: A. Viegas]
#5618624 - 01/12/13 08:57 AM

Bump.

I got an email recently from someone asking if I could add Duncan masks to my lineup, so I wanted to see if that would be a useful service to provide to the community. I've read some conflicting posts here about people being able to get results with them, and I've never owned an SCT so I don't know if methods like Greg Nowell's SGCD are easier/better. I don't want to sell something to people that isn't going to work well.

Post Extras:

m2k
member

Reged: 12/10/06

Loc: Massachusetts, USA

Re: Why no commercial source for "Duncan" Mask? new

[Re: jbalsam]
#5622196 - 01/14/13 07:16 AM

Mary B. (Echo Astronomy and Electronics) in a previous post stated that these masks can be laser cut up to 10" in diameter...
I'm wondering if a larger diameter disc can be used to "stop-down" a larger diameter scope to 10" and still work? I'm thinking here of my C-14.

-Mike

Post Extras:

Pages: 1 | 2 | 3 | 4 | (show all)

Extra information

17 registered and 16 anonymous users are browsing this forum.

Moderator: Cotts, Starman27

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled

Thread views: 5800

Jump to

CN Forums

Home

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics